A disease similar to bancroftian filariasis is produced by a closely related filarial worm, Brugia nnalayi. The sheathed microfilariae of this species have two distinct caudal nuclei. Transmitted by mansonoides mosquitoes, it is the only filarial infection of man in Malaya and Borneo, whereas in India, Ceylon, and tropical China it coexists with W. bancrofti. Brugia malayi is responsible for only mild lymphedema in man, usually below the knee, with enlargement of the popliteal and femoral nodes. In contrast to bancroftian filariasis, the microfilaremia rates in the Malayan form are quite high in children younger than five years. In this infection, also, there are two types of organisms, one with nocturnal periodicity, and another subperiodic form. The latter is found in many animals (primates, carnivores, and rodents) and is a true zoonosis.